1. Field of the Invention
The present invention relates to a piezoelectric type vibrator, and more particularly to a floating mass-type piezoelectric vibrator having a simple structure, an implantable hearing aid having the same, and a method of implanting the hearing aid.
2. Background of the Related Art
A hearing aid can be classified into a conventional body-worn hearing aid and an implantable hearing aid. The conventional hearing aid has a merit in that it can be easily mounted at an auricle and/or an acoustic pore of an external ear. However, the conventional hearing aid also has a demerit in that it does not satisfy a performance specification required for those who have more than severe hearing loss. The implantable hearing aid is suited for individuals with such severe hearing impairment. Such an implantable hearing aid can be divided into an implantable middle ear hearing device (IMEHD) and an implantable inner ear hearing device (cochlear implant).
The implantable middle ear hearing device typically includes a microphone and a vibrator. The research on the implantable middle ear hearing device is conducted intensively in view of the fact that it can effectively transfer a sound signal to persons who have sensorineural hearing loss because of its simple structure.
A human's ear is divided into three parts: external ear, middle ear and inner ear. An external sound is transmitted to the brain in the form of sound wave signal while sequentially passing through these three ear parts. Among these ear parts, the middle ear includes a tympanic membrane, a tympanic cavity and an auditory ossicle that consists of three small bones known as malleus, an incus and stapes. A vibrator for the implantable middle ear hearing device is mounted at the auditory ossicle so that it transmits an external audio signal to the inner ear as an acoustic vibration signal.
Such a vibrator for the implantable middle ear hearing device can be classified into an electromagnetic-transducer type one and a piezoelectric type one.
As one example of a conventional electromagnetic-transducer type vibrator, the Korean patent Nos. 282066 and 282067 disclose an electronic transducer for hearing aids implanted in the middle ear, in which vibration is generated by using an electromagnetic repulsive force caused by a coil and a magnet.
FIG. 1 illustrates one example of an electromagnetic-transducer type vibrator according to the prior art. As shown in FIG. 1, the electromagnetic-transducer type vibrator 1 includes a case 10, a coil 30 arranged at the inside of the case 10, a pair of magnets 20a and 20b disposed within the case 10 in such a fashion that the magnets are partially surrounded by the coil 30, a pair of elastic members 40a and 40b each connected at one end thereof to the inner wall of the case 10 and connected at the other end thereof to one side of each of the magnets 20a and 20b. In this case, the magnets 20a and 20b are aligned such that identical magnetic poles thereof are opposite one another. When an acoustic current signal corresponding to an acoustic signal is applied to the coil 40 from the outside, the magnets 20a and 20b are vibrated in the transverse axial direction of the electromagnetic-transducer type vibrator owing to the interaction between the coil 30 and the magnets 20a and 20b. This vibration is transmitted to the case 10 through the elastic members 40a and 40b, which is in turn transmitted to the auditory ossicle at which the electromagnetic-transducer type vibrator is mounted. At this time, the auditory ossicle delivers an acoustic vibration signal to an auditory nerve cell. Such an electromagnetic-transducer type vibrator has an advantage in that since it is configured in a floating mass type, its installation is easy. That is, the electromagnetic-transducer type vibrator is mounted at the auditory ossicle by means of a clamping member like a clip as an external constitutional element, and hence its easy installation is possible. However, the electromagnetic-transducer type vibrator also has a problem in that it is not easy to manufacture since it includes complicated elements such as magnets aligned such that their identical poles are opposed to one another, a coil, a membrane, etc.
On the contrary, the piezoelectric type vibrator has a merit in that it is easy for accomplishing a desired purpose through relatively simple constitutional elements such as a lead wire for transmitting an external acoustic current signal to the inner ear, electrodes connected to the lead wire, a piezoelectric element disposed between the electrodes, etc. The piezoelectric type vibrator also has an advantage in that it is excellent in an acoustic vibration transmitting efficiency unlike the electromagnetic-transducer type vibrator having the magnets and the coil.
However, the conventional piezoelectric type vibrator also has a demerit in that it is difficult to mount. That is, in order to transmit the vibration generated from the piezoelectric type vibrator to the auditory ossicle, the vibrator must be fixedly connected at one end thereof to a certain region within the ear. For example, in case of a vibrator embedded in the Envoy® middle ear implantable system manufactured by St. Croix Medical Inc., the vibrator is mounted at one end thereof to one side of the tympanic bone and abuts the other end thereof against the auditory ossicle so that an acoustic vibration signal is transmitted to the auditory ossicle in response to the vibration of an piezoelectric element. However, such a conventional piezoelectric type vibrator still has a problem in that its mechanical construction is complicated which is designed for allowing an appropriate pressure to be maintained at the contact portions at the time of mounting one end of the vibrator to the tympanic bone and connecting its other end to the auditory ossicle, as well as allowing an otolaryngologist to easily perform the hearing aid implantation operation in a short time period.